Cell variants of human amnion cell lines will be examined for ability to produce measles virus and to harbor this virus in a persistent infection. The restriction of virus in that persistent infection will be examined in these and other cells to determine the possible cellular factors concerned with preventing full synthesis of infectious virions. The effect of interferon, previously noted to facilitate the establishment of persistent infection by paramyxoviruses, will be tested to determine what role this substance may play and whether established persistent infections can be modified by increasing the amounts of interferon added exogenously. The overall objective of this program is to determine factors involved in establishing persistent infection by paramyxoviruses, especially measles virus, and the role of such infections in human disease.